Etching method and apparatus

ABSTRACT

An etching apparatus comprises a workpiece holder ( 21 ) for holding a workpiece (X), a plasma generator ( 10, 20 ) for generating a plasma ( 30 ) in a vacuum chamber ( 3 ), an orifice electrode ( 4 ) disposed between the workpiece holder ( 21 ) and the plasma generator ( 10, 20 ), and a grid electrode ( 5 ) disposed upstream of the orifice electrode ( 4 ) in the vacuum chamber ( 3 ). The orifice electrode ( 4 ) has orifices ( 4   a ) defined therein. The etching apparatus further comprises a voltage applying unit ( 25, 26 ) for applying a voltage between the orifice electrode ( 4 ) and the grid electrode ( 5 ) to accelerate ions from the plasma ( 30 ) generated by the plasma generator ( 10, 20 ) and to pass the extracted ions through the orifices ( 4   a ) in the orifice electrode ( 4 ). A first collimated neutral particle beam is generated and applied to the workpiece (X) for etching a surface of a processing layer ( 60 ) of the workpiece (X). A second collimated neutral particle beam is generated, and a mask ( 50 ) for covering at least a portion of the surface of the processing layer ( 60 ) is sputtered by the second neutral particle beam to form a protecting film ( 80 ) on a sidewall ( 60   a ) of the processing layer ( 60 ) for protecting the sidewall ( 60   a ) of the processing layer ( 60 ) from being etched by the first neutral particle beam.

TECHNICAL FIELD

The present invention relates to an etching method and apparatussuitable for use in micromachining processes involved in the fabricationof semiconductor devices or the like, and more particularly to anetching method and apparatus for processing a surface of a workpiecewith use of a neutral particle beam generated by neutralizing positiveor negative ions generated in a plasma.

BACKGROUND ART

In recent years, semiconductor integrated circuits, micromachines, andthe like have been processed in highly fine patterns. Therefore, ahighly accurate process with a high selectivity and a process to form ahigh aspect ratio pattern are required. In the fields of suchprocessing, there has widely been used a plasma etching apparatus.

As a plasma etching apparatus, there has been known a reactive ionetching (RIE) apparatus which generates various kinds of particlesincluding positive ions and radicals. The positive ions or the radicalsare applied to a workpiece to etch the workpiece.

In an etching process utilizing such an RIE apparatus, there have beenproblems that high accuracy and high selectivity cannot be achievedsimultaneously and etching profile irregularities are caused by chargebuild-up. The selectivity is a ratio of the etched depth in a workpieceto the etched depth in a mask or an underlying material. Specifically,when a workpiece is etched by x μm and a mask protecting the workpieceis etched by y μm, the selectivity s is expressed by s=x/y. In the caseof a higher selectivity, the mask is less damaged and the workpiece canbe etched to form a pattern having a high aspect ratio.

In order to enhance the selectivity, a combination of gases which candeposit on the mask or the underlying material but can etch theworkpiece has been used in the conventional etching process. Further,radicals deposit onto the sidewall surface of the workpiece to form asidewall passivation layer. If the sidewall passivation layer isexcessively formed on the surface of the workpiece, then the surface ofthe workpiece is processed into a tapered shape, so that dimensionalaccuracy is lowered in the etching process. When a combination of Cl₂gas and O₂ gas is used in the conventional etching process, theselectivity of Si/SiO₂ is at most about 100. Thus, this combination ofgases can achieve a higher selectivity than other combinations of gases.However, devices having a pattern smaller than 0.1 μm have been requiredto be processed with high accuracy and a selectivity higher than 300.Particularly, it will be the future task to simultaneously achieve ahigher selectivity over an underlying layer of a gate oxide film and noresidue at step portions for isolation.

The etching profile irregularities are caused by the difference betweenthe behavior of electrons and that of positive ions. Specifically, theetching profile irregularities, i.e., notches, are produced at sidewallsdefining stripes of a fine pattern. When the etching process isperformed with a low energy ion beam, electrons are decelerated withinthe fine pattern by a negative self-bias potential on the workpiece, andtrapped near a resist. On the other hand, ions are accelerated anddelivered to the underlying layer of the oxide film to develop positivecharge build-up on the workpiece. However, at the outside of the finepattern, charge build-up is not developed because the same amounts ofelectrons and ions are delivered thereto and neutralized. Thus, apotential difference is produced between the inside and outside of thefine pattern, so that the trajectories of the ions are curved to producethe notches.

DISCLOSURE OF INVENTION

The present invention has been made in view of the above drawbacks. Itis therefore an object of the present invention to provide an etchingmethod and apparatus which can etch a surface of a workpiece withoutcharge build-up or etching profile irregularities on the workpiece, andcan simultaneously achieve high accuracy and high selectivity over amask or an underlying layer for a fine pattern.

According to a first aspect of the present invention, there is providedan etching method comprising: etching a surface of a processing layer ofa workpiece by generating a first collimated neutral particle beam froma first gas and applying the first neutral particle beam to theworkpiece; and forming a protecting film on a sidewall of the processinglayer for protecting the sidewall of the processing layer from beingetched by the first neutral particle beam. The first neutral particlebeam should preferably have an energy ranging from 10 eV to 50 eV.

According to the present invention, in the etching process, the surfaceof the processing layer is etched by the first neutral particle beamhaving no electric charges but having a large translational energyranging from 10 eV to 50 eV. Therefore, secondary electrons are notemitted from the surface of the processing layer, and hence theworkpiece can be etched with a lower charge build-up voltage. Further,since the collimated neutral particle beam is applied to the workpiece,the workpiece can highly accurately be etched even in the case where asidewall passivation layer is not formed on the surface of theprocessing layer. Specifically, the processing layer is hardly sputteredby the neutral particle beam having a low energy ranging form 10 eV to50 eV, and thermochemical reaction occurs between the neutral particlebeam and the processing layer. As a result, a reaction product isspontaneously sublimed on the processing layer to perform the etchingprocess. If the neutral particles have no directionality and executethermal motion, then the workpiece is isotropically etched. However,according to the present invention, since the neutral particle beam iscollimated, anisotropic etching can be achieved. When the neutralparticle beam has an energy ranging from 10 eV to 50 eV, a resist ishardly sputtered by the neutral particle beam. Therefore, the workpiececan be etched with high selectivity.

When an ion beam having a low energy is applied to the workpiece in aconventional RIE apparatus, the ion beam may be curved due to anelectric field produced by charge unbalance between ions and electronswithin a fine pattern, so that notches may be produced as local etchingprofile irregularities. According to the present invention, however,since the etching method utilizes a neutral particle beam, it ispossible to etch the workpiece to form a pattern having a high aspectratio without generating notches.

In the forming process, the protecting film can be formed on thesidewall of the processing layer for protecting the sidewall of theprocessing layer from being etched by the first neutral particle beam.Therefore, a highly accurate etching process can be achieved in such astate that the sidewall of the processing layer is prevented from beingetched by the first neutral particle beam. Thus, the etching methodaccording to the present invention can simultaneously achieve highaccuracy and high selectivity for a fine pattern.

According to a preferred aspect of the present invention, the etchingmethod further comprises covering at least a portion of the surface ofthe processing layer with a shielding member, the forming comprising:generating a second collimated neutral particle beam from the first gas;and sputtering the shielding member by the second neutral particle beamto form the protecting film on the sidewall of the processing layer. Thesecond neutral particle beam should preferably have an energy rangingfrom 50 eV to 200 eV.

According to a preferred aspect of the present invention, the formingcomprises: generating a second collimated neutral particle beam from asecond gas; and applying the second neutral particle beam to the surfaceof the processing layer to form the protecting film on the sidewall ofthe processing layer.

According to a preferred aspect of the present invention, the processinglayer comprises a silicon layer, the first gas includes SF₆, and thesecond gas includes a fluorocarbon gas.

According to a preferred aspect of the present invention, the processinglayer comprises a silicon layer, and a layer underlying the processinglayer comprises a silicon oxide film; wherein the forming is performedimmediately before the etching is completed, and then the etching isperformed again.

Thus, the present invention is suitable for use in a gate etchingprocess in which the processing layer comprises a silicon layer and alayer underlying the processing layer comprises a silicon oxide film.According to the present invention, a gate etching process with a highselectivity can be performed without any residues or any damages on theworkpiece.

According to a preferred aspect of the present invention, the etchingmethod further comprises removing the protecting film formed on thesidewall of the processing layer.

According to a preferred aspect of the present invention, the etchingmethod further comprises repeating the etching, the removing, and theforming.

According to a second aspect of the present invention, there is providedan etching apparatus comprising: a workpiece holder for holding aworkpiece; a plasma generator for generating a plasma in a vacuumchamber; a first electrode disposed between the workpiece holder and theplasma generator, the first electrode having orifices defined therein; asecond electrode disposed upstream of the first electrode in the vacuumchamber; and a voltage applying unit for applying a voltage between thefirst electrode and the second electrode to accelerate ions from theplasma generated by the plasma generator and to pass the extracted ionsthrough the orifices in the first electrode; wherein a first collimatedneutral particle beam is generated and applied to the workpiece foretching a surface of a processing layer of the workpiece; wherein asecond collimated neutral particle beam is generated, and a shieldingmember for covering at least a portion of the surface of the processinglayer is sputtered by the second neutral particle beam to form aprotecting film on a sidewall of the processing layer for protecting thesidewall of the processing layer from being etched by the first neutralparticle beam. The first neutral particle beam should preferably have anenergy ranging from 10 eV to 50 eV. The second neutral particle beamshould preferably have an energy ranging from 50 eV to 200 eV.

According to a preferred aspect of the present invention, the etchingapparatus further comprises an end point detector for detecting an endpoint of an etching process.

According to a third aspect of the present invention, there is providedan etching apparatus comprising: a workpiece holder for holding aworkpiece; a plasma generator for generating a plasma in a vacuumchamber; a first electrode disposed between the workpiece holder and theplasma generator, the first electrode having orifices defined therein; asecond electrode disposed upstream of the first electrode in the vacuumchamber; and a voltage applying unit for applying a voltage between thefirst electrode and the second electrode to accelerate ions from theplasma generated by the plasma generator and to pass the extracted ionsthrough the orifices in the first electrode; wherein a first collimatedneutral particle beam is generated and applied to the workpiece foretching a surface of a processing layer of the workpiece; wherein asecond collimated neutral particle beam is generated, and the firstelectrode is sputtered by the second neutral particle beam to form aprotecting film on a sidewall of the processing layer for protecting thesidewall of the processing layer from being etched by the first neutralparticle beam. The first neutral particle beam should preferably have anenergy ranging from 10 eV to 50 eV. The second neutral particle beamshould preferably have an energy ranging from 50 eV to 200 eV.

According to a preferred aspect of the present invention, the etchingapparatus further comprises an end point detector for detecting an endpoint of an etching process.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a schematic view showing a whole arrangement of an etchingapparatus according to a first embodiment of the present invention;

FIG. 2A is a perspective view showing an orifice electrode in theetching apparatus shown in FIG. 1;

FIG. 2B is a vertical cross-sectional view partially showing the orificeelectrode shown in FIG. 2A;

FIGS. 3A and 3B are schematic views showing an etching process in theetching apparatus shown in FIG. 1;

FIGS. 4A and 4B are schematic views showing an example of an etchingprocess; and

FIG. 5 is a schematic view showing a whole arrangement of an etchingapparatus according to a second embodiment of the present invention.

BEST MODE FOR CARRYING OUT THE INVENTION

An etching apparatus according to embodiments of the present inventionwill be described in detail below with reference to FIGS. 1 through 5.Like or corresponding components are denoted by like or correspondingreference numerals throughout drawings, and will not be described belowrepetitively.

FIG. 1 is a schematic view showing a whole arrangement of an etchingapparatus according to a first embodiment of the present invention, withelectric components in block form. As shown in FIG. 1, the etchingapparatus comprises a cylindrical vacuum chamber 3 constituted by a beamgenerating chamber 1 for generating a neutral particle beam and aprocess chamber 2 housing therein a workpiece X such as a semiconductorsubstrate, a glass workpiece, an organic workpiece, or a ceramicworkpiece. The beam generating chamber 1 of the vacuum chamber 3 haswalls made of quartz glass or ceramics, and the process chamber 2 of thevacuum chamber 3 has walls made of metal.

The beam generating chamber 1 has a coil 10 disposed therearound forinductively coupled plasma (ICP). The coil 10 is housed in awater-cooled tube having an outside diameter of about 8 mm, for example.The coil 10 of about two turns is wound around the beam generatingchamber 1. The coil 10 is electrically connected to a high-frequencypower supply 20, which applies a high-frequency voltage having afrequency of about 13.56 MHz, for example, to the coil 10. When ahigh-frequency current is supplied from the high-frequency power supply20 to the coil 10, an induced magnetic field is produced in the beamgenerating chamber 1 by the coil 10. The varying magnetic field inducesan electric field, which accelerates electrons to generate a plasma 30in the beam generating chamber 1. Thus, the coil 10 and thehigh-frequency power supply 20 constitute a plasma generator forgenerating a plasma 30 in the beam generating chamber 1.

The beam generating chamber 1 has a gas inlet port 11 defined in anupper portion thereof for introducing a gas into the beam generatingchamber 1. The gas inlet port 11 is connected through a gas supply pipe12 to a gas supply source 13, which supplies a gas such as SF₆, CHF₃,CF₄, Cl₂, Ar, O₂, N₂, C₄F₈, CF₃I, and C₂F₄ to the beam generatingchamber 1.

The process chamber 2 houses a workpiece holder 21 therein for holdingthe workpiece X. The workpiece X is placed on an upper surface of theworkpiece holder 21. The process chamber 2 has a gas outlet port 22defined in a sidewall thereof for discharging the gas from the processchamber 2. The gas outlet port 22 is connected through a gas outlet pipe23 to a vacuum pump 24, which operates to maintain the process chamber 2at a predetermined pressure.

The process chamber 2 has an end point detector 40 provided at thesidewall thereof for monitoring the etching process and detecting an endpoint of the etching process. The end point detector 40 may comprise aquadrupole mass spectrometer, for example. Alternatively, the end pointdetector 40 may utilize laser interference or ellipsometry to detect anend point of the etching process.

An orifice plate (orifice electrode) 4 made of an electricallyconductive material such as graphite is disposed as a first electrode inthe lower end of the beam generating chamber 1. The orifice electrode 4is electrically connected to a DC power supply 25. FIG. 2A is aperspective view showing the orifice electrode 4, and FIG. 2B is avertical cross-sectional view partially showing the orifice electrode 4shown in FIG. 2A. As shown in FIGS. 2A and 2B, the orifice electrode 4has a number of orifices 4 a defined therein. Typically, the orificeelectrode 4 has a number of orifices 4 a each having a diameter of 1 mmand a length of 10 mm, and the orifices 4 a are arranged with a pitch of1.4 mm. The beam generating chamber 1 is separated from the processchamber 2 by the orifice plate 4. Therefore, the pressure of the processchamber 2 can be set to be lower than that of the beam generatingchamber 1 with the vacuum pump 24.

An electrode 5 made of an electrically conductive material is disposedas a second electrode in the upper end of the beam generating chamber 1.The electrode 5 is electrically connected to a DC power supply 26. Theelectrode 5 may comprise a plate made of metal, silicon, or graphite andhaving no holes. Alternatively, the electrode 5 may comprise a platehaving a number of holes defined therein for introducing the gasuniformly into the beam generating chamber 1. The DC power supply 25 andthe DC power supply 26 constitute a voltage applying unit for applying avoltage between the orifice electrode 4 and the electrode 5.

Operation of the etching apparatus according to the present embodimentwill be described below. In the present embodiment, an etching process(gate etching process) of etching a polycrystalline silicon layer formedon a silicon oxide film of a semiconductor substrate will be describedas an example.

The vacuum pump 24 is driven to evacuate the vacuum chamber 3, and thena gas such as SF₆ is introduced from the gas supply source 13 into thebeam generating chamber 1. For example, the pressure in the beamgenerating chamber 1 is set to be 0.1 Pa, and the pressure in theprocessing chamber 2 is set to be 1 Pa. A high-frequency voltage havinga frequency of about 13.56 MHz is applied to the coil 10 for 50microseconds by the high-frequency power supply 20, so that ahigh-frequency electric field is produced in the beam generating chamber1. The gas introduced into the beam generating chamber 1 is ionized byelectrons that are accelerated by the high-frequency electric field, forthereby generating a high-density plasma 30 in the beam generatingchamber 1. The plasma 30 is mainly composed of positive ions and heatedelectrons.

Then, the high-frequency voltage applied by the high-frequency powersupply 20 is interrupted for 50 microseconds. As a result, the electrontemperature is lowered by inelastic collision of the electrons, and theelectrons are attached to the residual process gas to generate negativeions. Thereafter, the high-frequency voltage is applied again to thecoil 10 for 50 microseconds by the high-frequency power supply 20 toheat the electrons in the plasma in the beam generating chamber 1. Thus,the above cycle is repeated. In this manner, the application of thehigh-frequency voltage for 50 microseconds and the interruption of thehigh-frequency voltage for 50 microseconds are alternately repeated. Theperiod of time (50 microseconds) for which the high-frequency voltage isinterrupted is sufficiently longer than a period of time in which theelectrons in the plasma 30 are attached to the residual process gas togenerate negative ions, and sufficiently shorter than a period of timein which the electron density in the plasma 30 is lowered to extinguishthe plasma. The period of time (50 microseconds) for which thehigh-frequency voltage is applied is long enough to recover the energyof the electrons in the plasma 30 which has been lowered during theinterruption of the high-frequency voltage.

While ordinary plasmas are mostly composed of positive ions andelectrons, the etching apparatus according to the present embodiment canefficiently generate a plasma in which positive ions and negative ionscoexist therein. Although the high-frequency voltage is interrupted for50 microseconds in the above example, it may be interrupted for a periodof time ranging from 50 to 100 microseconds to generate a large quantityof negative ions as well as positive ions in the plasma.

The DC power supply 25 applies a voltage of −50 V to the orifice plate4, and the DC power supply 26 applies a voltage −100 V to the electrode5. Accordingly, a potential difference is produced between the orificeelectrode 4 and the electrode 5. Therefore, as shown in FIG. 2B, thenegative ions 6 generated in the beam generating chamber 1 areaccelerated toward the orifice electrode 4 by the potential differenceand introduced into the orifices 4 a defined in the orifice electrode 4.Most of the negative ions 6 that are passing through the orifices 4 a inthe orifice electrode 4 are collided with the sidewall surfaces of theorifices 4 a and hence neutralized in the vicinity of solid sidewallsurfaces of the orifices 4 a, or are collided with gas moleculesremaining within the orifices 4 a and hence neutralized by chargeexchange with the gas molecules. Thus, the negative ions are convertedinto neutral particles (fluorine atoms) 7.

The orifice electrode 4 serves not only to neutralize the ions, but alsoto collimate the neutral particle beam and further to separate the beamgenerating chamber 1 and the process chamber 2 from each other. Theworkpiece can highly accurately be etched with the collimated neutralparticle beam. Since the beam generating chamber 1 and the processchamber 2 are separated from each other, the pressure of the processchamber 2 can be set to be lower than the pressure of the beamgenerating chamber 1, so that the accurate etching can be achieved.Further, the orifice electrode 4 which separates the beam generatingchamber 1 and the process chamber 2 from each other can prevent aradiation produced by the plasma from being applied to the workpiece X.Specifically, since the beam generating chamber 1 where the plasma isgenerated is isolated from the workpiece X by the orifice electrode 4,the radiation produced by the plasma is not substantially applied to theworkpiece X. Therefore, it is possible to reduce adverse effects on theworkpiece X due to the radiation such as an ultraviolet ray which wouldotherwise damage the workpiece X.

As described above, the negative ions that have been neutralized whenpassing through the orifices 4 a, i.e., fluorine atoms, are emitted asan energetic beam having a low energy into the process chamber 2. Thefluorine atoms travel directly in the process chamber 2 and are appliedto the workpiece (semiconductor substrate) X placed on the workpieceholder 21. As shown in FIG. 3A, the fluorine atoms applied to theworkpiece X are spontaneously sublimed as SiF₄ on the processing layer(polycrystalline silicon layer) 60 of the workpiece X according to thefollowing thermochemical equation.Si+4F→SiF₄↑Thus, the etching process is performed at portions of thepolycrystalline silicon layer 60 which are not covered with a mask 50.As shown in FIG. 3A, the etching portion has a sidewall 60 a formed inthe polycrystalline silicon layer 60. Although the mask 50 is a resistmade of organic matter, the mask 50 is not sputtered by the beam becausethe beam has a low energy. The beam for etching the polycrystallinesilicon layer 60, i.e., a first neutral particle beam, should preferablyhave an energy ranging from 10 eV to 50 eV.

In this etching process, the end point detector 40 detects an end pointof the process. When the end point detector 40 detects an end point ofthe etching process (immediately before or immediately after the siliconoxide film 70 is exposed), the DC power supply 25 changes the voltage tobe applied to the orifice electrode 4 from |50 V to +100 V, for example.The change of the voltage applied to the orifice electrode 4 increasesthe energy of the beam emitted into the process chamber 2. Therefore,the mask 50 made of organic matter is sputtered by the beam having anincreased energy, for thereby forming an organic film 80 of CH_(x)F_(y)on the sidewall 60 a of the polycrystalline silicon layer 60 as shown inFIG. 3B. Thus, the sidewall 60 a of the polycrystalline silicon layer 60is covered with the organic film 80. The organic film 80 serves as aprotecting film for protecting the sidewall 60 a of the polycrystallinesilicon layer 60 from being etched by the fluorine atoms. The beam forforming the protecting film 80, i.e., a second neutral particle beam,should preferably have an energy ranging from 50 eV to 200 eV.

After the organic film 80 having a predetermined thickness is depositedon the sidewall 60 a of the polycrystalline silicon layer 60, the DCpower supply 25 changes the voltage to be applied to the orifice plate 4from +100 V to −50 V. As a result, an energetic beam (the first neutralparticle beam) having a low energy and a high reactivity is emittedagain into the process chamber 2. Since the protecting film 80 has beendeposited on the sidewall 60 a of the polycrystalline silicon layer 60,the sidewall 60 a of the polycrystalline silicon layer 60 is not etchedby the beam. Therefore, the highly accurate etching process can beachieved. Since the etching process in the present embodiment utilizes Fradicals which are more reactive than Cl radicals or Br radicals, theetching rate can be increased.

As shown in FIG. 4A, in the case of an etching process (gate etchingprocess) of etching a polycrystalline silicon layer 110 formed on anunderlying silicon oxide film 100 with use of a collimated fluorineneutral particle beam having an energy ranging from 10 eV to 50 eV, thepolycrystalline silicon layer 110 is etched in a vertical directionaccording to the following thermochemical equation.Si+4F→SiF₄↑Since the silicon oxide film 100 does not react with the fluorine atoms,even if the etching process is performed until the silicon oxide film100 is exposed, the silicon oxide film 100 is not etched by the beam.Therefore, the workpiece X can be etched with a high selectivity ofSi/SiO₂. In this case, however, the sidewall 110 a of thepolycrystalline silicon layer 110 may be etched by the fluorine atomsreflected on the surface 100 a of the silicon oxide film 100, resultingin etching profile irregularities, as shown in FIG. 4B. According to thepresent embodiment, as shown in FIG. 3B, the mask 50 is sputtered toform the protecting film 80 on the sidewall 60 a of the polycrystallinesilicon layer 60 for protecting the sidewall 60 a of the polycrystallinesilicon layer 60 from being etched by the fluorine neutral particlebeam. Therefore, according to the present embodiment, it is possible toprevent the aforementioned etching profile irregularities from beingcaused by the fluorine neutral particle beam.

In the present embodiment, the mask 50 is sputtered to form theprotecting film 80 on the sidewall 60 a of the polycrystalline siliconlayer 60. Instead of the mask 50, other shielding members may be usedfor covering at least a portion of the surface of the processing layer.For example, an orifice electrode 4 made of graphite is sputtered togenerate a CF_(x) beam, for thereby forming the protecting film on thesidewall of the processing layer. Alternatively, a meshed shieldingplate made of organic matter may be inserted between the orificeelectrode 4 and the workpiece X, and the shielding plate may besputtered to form the protecting film on the sidewall of the processinglayer.

FIG. 5 is a schematic view showing a whole arrangement of an etchingapparatus according to a second embodiment of the present invention,with electric components in block form. As shown in FIG. 5, a gas inletport 11 is connected through two branched gas supply pipes 12 a, 12 b togas supply sources 13 a, 13 b. The gas supply source 13 a supplies afirst gas such as SF₆ to the beam generating chamber 1, and the gassupply source 13 b supplies a second gas such as a fluorocarbon (C₄F₈,CHF₃, C₂F₄, or the like) to the beam generating chamber 1. The gassupply pipes 12 a, 12 b have valves 15 a, 15 b provided thereon,respectively.

Operation of the etching apparatus according to the present embodimentwill be described below. First, the valve 15 b of the gas supply pipe 12b is closed, and the valve 15 a of the gas supply pipe 12 a is opened.As a result, an etching gas such as SF₆ is introduced from the gassupply source 13 a into the beam generating chamber 1. As with the firstembodiment, a first neutral particle beam (fluorine atom beam) isgenerated from the plasma 30 in the beam generating chamber 1 andemitted into the processing chamber 2. Portions of a polycrystallinesilicon layer which are not covered with a mask are etched by theneutral particle beam having a low energy ranging from 10 eV to 50 eV.

When an end point of the etching process is detected by the end pointdetector 40, the valve 15 a of the gas supply pipe 12 a is closed andthe valve 15 b of the gas supply pipe 12 b is opened. As a result, a gassuch as C₄F₈, CHF₃, or C₂F₄ is introduced from the gas supply source 13b into the beam generating chamber 1. Positive ions (CF_(x) ⁺ such CF₂⁺, CF⁺, or CF₃ ⁺) are generated from the plasma 30 in the beamgenerating chamber 1. The positive ions are accelerated and neutralizedto generate a second neutral particle beam. The neutral particle beam isemitted into the processing chamber 2, for thereby forming a polymericfilm of CF_(x) on a sidewall of the polycrystalline silicon layer. Thus,the sidewall of the polycrystalline silicon layer is covered with thepolymeric film. The polymeric film serves as a protecting film forprotecting the sidewall of the polycrystalline silicon layer from beingetched by the fluorine atoms as with the organic film 80 in the firstembodiment.

After the protecting film having a predetermined thickness is depositedon the sidewall of the polycrystalline silicon layer, the valve 15 b ofthe gas supply pipe 12 b is closed and the valve 15 a of the gas supplypipe 12 a is opened. As a result, the etching gas is introduced into thebeam generating chamber 1, and hence the first neutral particle beam(fluorine atom beam) is emitted into the processing chamber 2. Since theprotecting film of CF_(x) has been deposited on the sidewall of thepolycrystalline silicon layer, the sidewall of the polycrystallinesilicon layer are not etched by the beam. Therefore, the highly accurateetching process can be achieved.

In the first and second embodiment described above, the etching processof the processing layer and the forming process of the protecting filmmay be repeated. In this case, the protecting film is not necessarilycompletely removed by the etching process, and hence the residualprotecting film may be formed into a tapered shape. In order to preventthe protecting film from having a tapered shape, the protecting film maybe removed from the sidewall of the processing layer after the etchingprocess of the processing layer before the forming process of theprotecting film. For example, if a TEOS film is used as a mask and O₂gas is introduced into the processing chamber 2, then the protectingfilm can be ashed by O₂ radicals. Thus, the protecting film can beremoved from the sidewall of the processing layer without etching themask or the processing layer.

Some charged particles may pass through the orifices 4 a in the orificeelectrode 4. In order to prevent such charged particles from beingapplied to the workpiece X, a deflector or an electron trap may bedisposed downstream of the orifice electrode 4. A voltage is applied tothe deflector in a direction perpendicular to a beam traveling directionto change the traveling direction of charged particles, for therebypreventing the charged particles from being applied to the workpiece X.The electron trap produces a magnetic field of about 100 gauss in adirection perpendicular to a beam traveling direction to change thetraveling direction of electrons, for thereby preventing the electronsfrom being applied to the workpiece X.

As well known in the art, when an insulated workpiece such as aworkpiece made of glass or ceramics is processed, charge build-up may bedeveloped on the surface of the insulated workpiece. However, byapplying neutralized particles to the insulated workpiece as describedabove, various processes including an etching process and a depositionprocess can highly accurately be performed on the insulated workpiecewith a low charge build-up voltage being maintained. Various types ofgases may be introduced into the beam generating chamber 1 according tothe type of process to be performed on the workpiece X. For example, ina dry etching process, oxygen or a halogen gas may selectively be usedaccording to the kind of the workpiece X.

In the above embodiment, the plasma is generated with use of a coil forICP. However, the plasma may be generated with use of an electroncyclotron resonance source (ECR source), a coil for helicon wave plasma,a microwave, or the like. The frequency of the high-frequency voltage isnot limited to 13.56 MHz, but may be in the range from 1 MHz to 20 GHz.The voltages applied to the orifice electrode 4 and the electrode 5 arenot limited to the above examples.

Although certain preferred embodiments of the present invention havebeen shown and described in detail, it should be understood that variouschanges and modifications may be made therein without departing from thescope of the appended claims.

INDUSTRIAL APPLICABILITY

The present invention is applicable to an etching method and apparatussuitable for use in micromachining processes involved in the fabricationof semiconductor devices or the like.

1. An etching method comprising: etching a surface of a processing layerof a workpiece by generating a first collimated neutral particle beamfrom a first gas and applying said first neutral particle beam to theworkpiece; and forming a protecting film on a sidewall of saidprocessing layer by a second collimated neutral particle beam to protectthe sidewall of said processing layer from being etched by said firstneutral particle beam; and covering at least a portion of the surface ofsaid processing layer with a shielding member, said forming comprising:generating said second collimated neutral particle beam from said firstgas; and sputtering said shielding member by said second neutralparticle beam to form the protecting film on the sidewall of saidprocessing layer.
 2. An etching method according to claim 1, whereinsaid first neutral particle beam has an energy ranging from 10 eV to 50eV.
 3. An etching method according to claim 1, wherein said secondneutral particle beam has an energy ranging from 50 eV to 200 eV.
 4. Anetching method according to claim 1, wherein said forming comprises:generating said second collimated neutral particle beam from a secondgas; and applying said second neutral particle beam to the surface ofsaid processing layer to form the protecting film on the sidewall ofsaid processing layer.
 5. An etching method according to claim 4,wherein said processing layer comprises a silicon layer, said first gasincludes SF₆, and said second gas includes a fluorocarbon gas.
 6. Anetching method according to claim 1, wherein said processing layercomprises a silicon layer, and a layer underlying said processing layercomprises a silicon oxide film; wherein said forming is performedimmediately before said etching is completed, and then said etching isperformed again.
 7. An etching method according to claim 1, furthercomprising: removing said protecting film formed on the sidewall of saidprocessing layer.
 8. An etching method according to claim 7, furthercomprising repeating said etching, said removing, and said forming. 9.An etching method comprising: etching a surface of a processing layer ofa workpiece by generating a first collimated neutral particle beam froma first gas and applying said first neutral particle beam to theworkpiece; and sputtering an electrode, which is used to generate aneutral particle beam, by a second collimated neutral particle beam toform a protecting film on a sidewall of said processing layer to protectthe sidewall of said processing layer from being etched by said firstneutral particle beam.
 10. An etching method according to claim 9,wherein said first neutral particle beam has an energy ranging from 10eV to 50 eV.
 11. An etching method according to claim 9, wherein saidsecond neutral particle beam has an energy ranging from 50 eV to 200 eV.12. An etching method according to claim 9, wherein said second neutralparticle beam is generated from a second gas.
 13. An etching methodaccording to claim 12, wherein said processing layer comprises a siliconlayer, said first gas includes SF6, and said second gas includes afluorocarbon gas.
 14. An etching method according to claim 9, whereinsaid processing layer comprises a silicon layer, and a layer underlyingsaid processing layer comprises a silicon oxide film; wherein saidsputtering is performed immediately before said etching is completed,and then said etching is performed again.
 15. An etching methodaccording to claim 9, further comprising removing said protecting filmformed on the sidewall of said processing layer.
 16. An etching methodaccording to claim 15, further comprising repeating said etching, saidremoving, and said sputtering.